1. Field of the Invention
The present invention generally relates to electrophotography and more particularly, to a developing apparatus for use in an image forming apparatus such as a copying apparatus or the like.
2. Description of the Prior Art
Conventionally, there has been proposed a multi-color copying apparatus, a multi-color printer or the like as one example of an image forming apparatus including electrophotographic copying means. Such an image forming apparatus is provided with a plurality of developing apparatus storing therein developer of several colors at the circumference of an electrostatic latent image support member or a photoreceptor drum, thereby reproducing an image formed on an original document, using several different colors.
However, at the circumference of the photoreceptor drum are disposed various kinds of appliances such as a charger, a cleaning device, an eraser and so on adjacent to one another. Because of this, the image forming apparatus generally used can accommodate only a few developing apparatuses adjacent to the photoreceptor drum.
If a large-sized photoreceptor drum is employed for the multi-color purpose, the image forming apparatus tends to become large. This fact goes against the recent demand for an apparatus of a small and compact size.
Japanese Patent Laid-open Application (Tokkaisho) No. 61-201271 discloses a multi-color developing apparatus of a small size. This developing apparatus is internally provided with a developing sleeve holding magnetic carrier on its peripheral surface, a cylindrical developer tank rotatably disposed at a side portion of the developing sleeve and the like. The inside of the developer tank is divided, in its several radial directions, into a plurality of compartments storing therein toner of several different colors. A plurality of toner supply and collecting rollers are rotatably disposed in respective openings formed at outside portions of the compartments so as to be able to confront the developing sleeve in the vicinity thereof.
In the above described developing apparatus, upon rotation of the developer tank, the toner supply and collecting roller in the developer compartment storing therein the toner of a specified color is caused to confront the developing sleeve so that the toner of the specified color may be supplied onto the developing sleeve. When the color of toner is changed, the toner held on the developing sleeve is initially collected into the developer compartment confronting it. Thereafter, upon rotation of the developer tank, the toner of another desired color is supplied from the developer compartment storing therein this toner onto the developing sleeve.
However, in the developing apparatus of the above described type in which the toner is supplied from the toner supply and collecting roller with respect to the carrier held on the developing sleeve, the toner can not be effectively supplied or collected unless a gap is accurately formed between the developing sleeve and the toner supply and collecting roller. Accordingly, the developing apparatus of this type is disadvantageous in that a mechanism for rotating the developer tank or for controlling its stop position becomes complicated.
Furthermore, when one of the developer compartments and one of the toner supply and collecting rollers confront the developing sleeve, one of the other compartments and rollers is located below. As a result, the toner often drops out of the developer compartment or from the surface of the roller. Such toner is liable to be supplied onto the developing sleeve upon rotation of the developer tank or to be collected into the developer compartment storing therein the toner of a different color, thus resulting in that two or more colors are disadvantageously mixed in a copied image.
Moreover, since the toner can not be replenished from a hopper or the like, the developer tank itself has to be detached from the developing apparatus for replenishment of the toner. Therefore, the apparatus of this type is disadvantageous in that the work for replenishing the toner becomes troublesome and the toner soils cloths or the human body.
This apparatus is also disadvantageous in that the color of toner can not be speedily changed, since it is necessary to rotate the developer tank in this occasion.